1. Field of the Invention
The present invention relates to a starter device for internal combustion engines of automotive vehicles, and more particularly to an output structure thereof.
2. Description of the Related Art
FIG. 1 shows the output structure of a conventional starter device for the internal combustion engine of automobiles. The starter device, generally designated by reference numeral 1, comprises a front housing frame 2a and a rear housing frame 2b coupled to each other to form the housing of the device. The output structure of the starter comprises an output shaft 3 which is operatively connected with and driven by a motor, and an axially slidable hollow cylindrical assembly disposed coaxially around and driven by the shaft 3. The output shaft 3 may be a rotary shaft of a motor. The axially slidable assembly comprises a hollow shaft 4, an overrunning clutch 5, a pinion-carrying hollow cylinder 6, and a pinion 6a, and is slidable on the shaft 3 in the axial direction between a front position at which the pinion 6a engages a ring gear 7 of an engine (not shown) and a rear position at which the pinion 6a is out of engagement therewith.
The output shaft 3 rotatably supported by the housing has a stopper 3a fixed at the front end thereof to limit the axial translation of the axially slidable assembly. The enlarged diameter portion 3b, which is formed on the shaft 3 at an axial position thereof which is situated at the rear of the overrunning clutch 5 when the clutch 5 is in the rear position, has helical splines formed at the outer circumferential surface thereof. A portion 3c of the shaft 3 in front of a step at the front end of an enlarged diameter portion 3b is plated, for example, with chromium, to prevent the development of rust, etc.
The axially slidable assembly, on the other hand, is constructed as follows. The hollow shaft 4 engages the output shaft 3 by means of helical keyways which are formed in the interior surface thereof and mesh with the helical splines formed on the enlarged diameter portion 3b of the shaft 3. Thus, the hollow shaft 4 is slidable on the shaft 3 in the axial direction. The overrunning clutch 5 comprises an outer member 5a integral with the hollow shaft 4, an inner member 5c integral with the pinion carrying hollow cylinder 6, and a friction rollers 5b interposed therebetween to transmit a rotational driving force in one rotational direction. The pinion-carrying hollow cylindrical member 6 is rotatably supported by the shaft 3 by means of a sleeve bearing 6b which is fitted on the interior circumferential surface of the pinion-carrying cylinder 6 and is slidable on the shaft 3 in the axial direction. Further, the pinion-carrying cylinder 6 is rotatably supported by the front housing frame 2a through a ball bearing 2c to be slidable in the axial direction. The shift lever 8 slides the overrunning clutch 5 along the shaft 3 in the axial direction.
The operation of the starter device of FIG. 1 is as follows. When the internal combustion engine (not shown) is to be started, the shift lever 8 is activated to move the slidable output assembly (including the hollow shaft 4, the overrunning clutch 5 and the pinion-carrying cylinder 6) to the front limit position at which the front end of the pinion-carrying cylinder 6 abuts the stopper 3a and the pinion 6a engages the ring gear 7 of the engine. When the motor is energized, the rotational force of the output shaft 3, which is operatively connected with and driven by the motor or which may be the rotary shaft of the motor, is transmitted to the hollow shaft 4 splined thereto, and thence to the pinion-carrying cylinder 6 through the overrunning clutch 5. Thus, the pinion 6a engaging with the ring gear 7 drives and rotates it to start the engine. After the engine is thus started, the slidable output assembly including the pinion carrying cylinder 6 returns to its rear position.
The output structure of the starter of FIG. 1 has following disadvantage. The plating on the outer circumferential surface of the portion 3c of the output shaft 3 which slidably supports the hollow cylinder 6 may come off in a relatively short time to develop rust thereon at exposed portions, due to the extremely severe environmental condition under which the portion 3c is; when this happens, the sliding movement of the pinion-carrying cylinder 6 on the shaft 3 is obstructed.
FIG. 2 shows a modified output structure of a starter device. A cap-shaped cover 9 is detachably fitted on an annular projection 6c formed at the front end of the pinion-carrying hollow cylinder 6, the cover 9 being coupled to the cylinder 6 at the open end portion thereof to close an opening 6f of the hollow cylinder 6 to the exterior space, and the inwardly turned annular end portion of the cap 9 being fitted into an annular groove 6dformed at the base of the projection 6c. The cover 9, which is moved with the pinion-carrying hollow cylinder 6 and has an axial length enough to accommodate the front portion of the output shaft 3 even when the pinion-carrying hollow cylinder 6 is retracted to its rear limit position, closes the opening 6f of the hollow cylinder 6 and prevents dust, foreign matter, etc., from entering into the interior of the opening 6f, thereby enhancing the durability of the sleeve bearings 6b and the portion 3c of the shaft 3 which slidably supports the hollow cylinder 6. Apart from the cover 9, the projection 6c and the groove 6d formed at the front end of the hollow cylinder 6, the output structure of FIG. 2 is similar to that shown in FIG. 1 except that the structure of FIG. 2 comprises an annular oil seal 2d interposed between the front housing frame 2a and the pinion-carrying hollow cylinder 6, and, further, that two sleeve bearings 6b instead of one are interposed between the shaft 3 and the hollow cylinder 6.
The output structure of the starter device shown in FIG. 2 suffers from following disadvantages:
(a) When the pinion 6a is in engagement with the ring gear 7 of the engine and the pinion-carrying hollow cylinder 6 is driven by the engine at a high speed, the cover 9 may be disengaged from the pinion-carrying cylinder 6, or damaged, due to the centrifugal force resulting from the rotation.
(b) When the starter device is to be attached to the engine, the cover 9 may be damaged by being struck by surrounding devices, etc.; in such cases, its proper function as a dust preventing cover may be lost, or a concave deformation resulting from the damage may obstruct the sliding movement of the pinion-carrying cylinder 6 on the shaft 3.
(c) The cover 9 moves forward with the pinion-carrying hollow cylinder 6 to project further forward from the front end of the output shaft 3 when the hollow cylinder 6 is slid to the front limit position. Thus, an additional space is needed for the cover 9 in front of the front end of the output shaft 3. Consequently, the starter device requires wider space in the engine room of the vehicle for its installation.